which should list all your network cards and their ip adresses. Usually is eth0 if you have a single network card.Notice: If you have connected to the internet using pppoeconf (broadband internet connection), the ip adress will be listed at ppp0.

2. If you want to find out what your ip adress which is connect to the internet:

ifconfig -a

which should list all your network cards and their ip adresses. If you can't see an Ip adress, then you should setup your network card.